Great trick! This was one of my favorites as a kid. I still have my original (from about 30 years ago). At one point the tape was eaten by my cassette player, and was never the same, but recently I was able to find someone to send me their tape, which I transferred to CD, on two tracks, enabling me to modernize it a bit.
Just a couple of weeks ago I found someone selling the trick; an original, but a later version with a slightly different recording, and small black plastic boxes to hold the weapons.